The opposition (other than WP who doesn't want "unity") has never been clear about the details of opposition unity, but we can see glimpses of it during the Punggol by election. SDP's definition is that the candidate is from SDP, while WP gives them the machinery. SDA as we already know is an empty alliance of but just 2 parties, i.e. to have an alliance in name.
(KJ of RP, as usual, is his schizophrenic self, lambasting WP for not wanting to discuss yet 2 days later labelled unity as a "far-fetched notion". So to date no one knows what he really stands for.)
In short, the smaller parties want the upper advantage in unity when negotiating with a bigger party. That makes me feel none of them are sincere.
In Malaysia, the parties within BN or Pakatan will compromise by their willingness to limit their own power, say or number of candidates for the sake of their alliances, with the smaller parties compromising more. Do you think UMNO or DAP cannot find 222 candidates on their own?